$ { {1} \times \left[\begin{array}{rr}{2} & {4} \\ {4} & {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{1}\times{2} & {1}\times{4} \\ {1}\times{4} & {1}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{2} & {4} \\ {4} & {-1}\end{array}\right]}$